$${\mathrm{2700\, \frac{kg}{m^3}=\frac{2700 \cdot 1\, kg}{1000\, dm^3}= 2,7\, \frac{kg}{dm^3}= \\ = \frac{2,7 \cdot 1000 \, g}{1\, dm^3} = 2700 \frac{g}{dm^3}}}$$